Modern wind turbines are commonly used to supply electricity into the electrical grid. Wind turbines generally comprise a rotor with a rotor hub and a plurality of blades. The rotor is set into rotation under the influence of the wind on the blades. The rotation of the rotor shaft drives the generator rotor either directly (“directly driven”) or through the use of a gearbox. The gearbox (if present), the generator and other systems are usually mounted in a nacelle on top of a wind turbine tower.
Pitch systems are normally employed for adapting the position of the blades to varying wind conditions. In this respect, it is known to rotate the position of each blade along its longitudinal axis in such a way that lift and drag are changed to reduce torque. This way, even though the wind speed increases, the torque transmitted by the rotor to the generator remains substantially the same. Using pitch systems may be particularly suitable for adapting the wind turbine blade to a varying wind speed. However, the control of the pitch systems may be rather slow and may not be suitable to react to a sudden wind gust or any other high rate changing wind conditions.
Some systems change the aerodynamics of a wind turbine blade by providing the blade with a trailing edge flap hinged to a main body. However, deflecting the aerodynamic surface about a hinged point may lead to flow separation which may cause abrupt aerodynamic changes thus decreasing load alleviation and reducing efficiency of the wind turbine.
Document WO2004/088130 describes the control of aerodynamic forces substantially instantaneously and locally along the blades of a wind turbine rotor by continuous variation of the airfoil geometry in the leading edge region and trailing edge region along part or the whole blade span. It further describes the use of smart materials or mechanical actuators integrated in a deformable material changing the outer geometry in the leading and trailing edge region and thereby changing the blade section aerodynamic forces.